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Research On Forced Lubrication Deep Drawing Process And Its Application In Box-Shaped Parts Forming

Posted on:2024-04-07Degree:DoctorType:Dissertation
Country:ChinaCandidate:D ChenFull Text:PDF
GTID:1521307151956619Subject:Materials Processing Engineering
Abstract/Summary:PDF Full Text Request
Sheet metal stampings are widely used in automobile manufacturing,aerospace,rail transportation and other fields for their performance advantage of lower mass to strength ratio.In matal forming,friction is one of the most important factors affecting the forming performance and quality.It is of great significance to deal with the friction problem to control the shape and performance of the product.During sheet metal deep drawing,high contact stress and wrinkling instability can lead to increased friction and difficult lubrication.The complex friction environment in sheet forming poses a significant challenge to the friction control and lubrication process during the production process.Based on the technical characteristics of forced lubrication,the following works have been carried out in the application of forced lubrication to sheet metal deep drawing:(1)In view of the difficult problem of high friction and poor lubrication in the flange area during deep drawing,a liquid medium forced lubrication process applied to the lubrication in the flange area is proposed,and its process principle,system composition and technical characteristics are described.The forced lubrication drawing process dies and supporting device are designed,and the experiments of forced lubrication drawing of box-shaped parts are carried out.Through process tests,it is verified that the forced lubrication deep drawing process proposed in this paper has advantages in improving forming performance,reducing forming force,suppressing thickness thinning and improving surface quality,and the quantitative evaluation is conducted.(2)The strip sliding friction tests under forced lubrication are carried out,and the influence of blank holder force and lubricant pressure on the friction coefficient is quantitatively investigated.A dynamic friction model of forced lubrication is constructed,and the model parameters are optimized by the genetic algorithm.Finally,the computational accuracy of the constructed dynamic friction model is evaluated by error analysis.The construction of the dynamic friction model of forced lubrication provides data support for the theoretical analysis and numerical simulation of the deformation process.(3)The mathematical expression of the stress in the flange area during box-shaped parts forced lubrication drawing process is derived based on the plastic deformation theory and forced lubrication friction model.The wrinkling critical blank holder force in the flange area during box-shaped part forced lubrication deep drawing is calculated using the partition calculation method combined with the energy method.Furthermore,the fracture critical blank holder force during box-shaped parts drawing is calculated by employing the stress expression and the criterion for the tensile instability of the sheet.According to the specific calculation example,the influence laws of forced lubrication on the stress distribution and critical blank holder force in the drawing process are investigated.The results indicate that lubrication and friction reduction in forced lubrication drawing play a major role in reducing the radial stress in the flange area and improving the forming limit,and the radial loading plays a secondary role.The application of forced lubrication increases the wrinkling critical blank holder force and fracture critical blank holder force.Finally,the reliability of the theoretical calculation model is verified by experiments.The theoretical calculation model provides the theoretical basis for product design,process optimization and intelligent control.(4)Based on the interface of VFRICTION subroutine of ABAQUS simulation platform,the dynamic friction model program of forced lubrication is written in FORTRAN language and applied to numerical simulation.The visual characterization of the coefficient of friction field variables of forced lubrication is realized through the coupling between VFRICTION and VUFIELD subroutines,which provides a basis for further research on the evolution of the coefficient of friction in the plastic deformation process.The fracture trajectory based on Lou-Huh ductile fracture criterion is constructed and implanted in the finite element model.The numerical simulations of the forced lubrication deep drawing process are performed in combination with the friction subroutine to investigate the effect of forced lubrication on the forming process.The results demonstrate that forced lubrication has a significant effect on reducing the friction coefficient,improving the forming limit,reducing the forming force and suppressing the thickness thinning.(5)The metal flow resistance in each region of flange is different during the deep drawing process of non-axisymmetric components represented by box-shaped parts,with large strain gradients and uneven deformation.Based on the technical advantages of the forced lubrication process and the mechanism of plastic deformation,a zoned forced lubrication process applied to the drawing of box-shaped parts is proposed.The local strain distribution is changed and the overall deformation uniformity is improved by frictional differentiation control in the flange area.It is verified that zoned lubrication has a positive effect on reducing the difference of metal flow rate and displacement in the flange area and weakening the effect of shear stress through numerical simulation.(6)The dies for zoned lubrication deep drawing are designed based on forced lubrication technology and the supporting oil supply system is developed.The zoned lubrication deep drawing experiments for box-shaped parts are conducted.In order to quantitatively evaluate the effect of differential lubrication on the deformation of box-shaped parts,the deformation uniformity evaluation indexes with the equivalent strain and thickness thinning rate as the relevant variables are established.The experimental results of zoned lubrication indicate that the value of strain and thickness thinning rate uniformity evaluation coefficient and dispersion degree tend to decrease with the increase of the forced lubrication pressure in the flange corner area.Process experiments and theoretical investigations have shown that the zoned lubrication process has a certain potential for improving the uniformity of deformation of complex-shaped components and improving the overall forming quality.
Keywords/Search Tags:sheet forming, forced lubrication, friction model, zoned lubrication, deformation uniformity
PDF Full Text Request
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